Selection of dosage: In man, D-serine is synthesized from L-serine via one enzymatic step catalyzed by the enzyme serine racemase. Levels of D-serine are controlled by the activity of serine racemase, the later having the highest expression in the forebrain. D-serine is currently being used in IND# 71,369 (D Javitt, PI). This approved serine will purchased by the Research Pharmacy at Johns Hopkins and encapsulated into capsules containing 250 and 500 mg of D-serine. The established treatment dose in the aforementioned IND is 30 mg/kg/day. In adults with schizophrenia and OCD, D-serine was safe and effective in dosages of 2 grams per day [Javitt Personal Communication].